1. Field of the Invention
The present invention relates generally to ultrasonic receiver apparatus, and more particularly to an ultrasonic receiver configured to be vandal-resistant in that it includes tamper-resistant fasteners, is a sturdy faceplate able to withstand repeated blows from any object potentially available to an inmate in a correctional or psychiatric facility, and has no unclosed passageways through which liquid or foreign objects may be passed.
2. Discussion of the Prior Art
Heretofore, ultrasonic transmitter/receiver apparatus has been used in duress alarm systems in settings such as hospitals, jails, courtrooms, warehouses, etc. to provide remote indication of an emergency situation. In such systems, a remote transmitter of an acoustical signal, typically in the form of a pen-like source or a small transmitter attached to the clothing of a person at risk, is used to generate an initiating ultrasonic distress signal which is then detected by a conventional ultrasonic receiver having a transducer mounted flush with the faceplate of the receiver or disposed behind perforations in the faceplate. Such positioning of the transducer allows the pressure wave generated by the source to impinge directly on the transducer and provide optimum sensitivity to the ultrasonic signal. However, the use of such a receiver in hostile environments exposes the transducer to damage by beating, poking or the injection of liquids that can destroy the unit or at the least inhibit its performance. Thus, historically, duress alarm systems have not been installed in patient rooms or cells because of the high maintenance cost and the lack of system reliability due to false alarms and malfunction.
In devices which operate in the audio spectrum, this problem has previously been addressed by building baffles and other complex geometric designs to provide physical barriers between the faceplate and the transducer. However, this results in a relatively expensive product. While it is clear that such an approach could work for applications using typical ultrasonic frequencies (namely, frequencies on the order of 43 KHz), it is not known that such an approach has been tried. As an alternative, attempts have been made to simply prevent access to the receiver. This either increases the cost of the installation or decreases the range or sensitivity of the receiver.
There is thus a need for a receiver that can be located in the room, cell or other environment of a secure facility where the clients, inmates, or prisoners have both time and opportunity to vandalize the unit.